The proposed applications that can benefit from cold and ultracold atom technology includes atom interferometry, quantum computing, nonlinear optics, atom interaction studies, atomic timekeeping, inertial navigation, magnetic sensing, and gravitational sensing. One serious obstacle to developing these applications has been the complexity and size of the vacuum systems required for ultracold atom production. Although recent scaled-down vacuum systems intended for producing Bose Einstein condensation (BEC) have begun to address this issue, there remains much that is still required in terms of miniaturization and reducing system complexity.
Active vacuum pumps like sputter-ion pumps and turbo pumps have become ubiquitous in cold and ultracold atom systems. In general, these pumps provide convenience, ease of use, and the ultra-high vacuum (UHV) conditions (10−8 torr to 10−13 torr) required for producing optically cooled and ultracold matter. A sputter ion pump works by ionizing vacuum impurities in the volume of the pump. A high voltage accelerates the ions toward the walls of the pump where they are sequestered via burial deep into the wall or by chemical reaction with the materials that form the wall. A turbo pump is a mechanical pump that uses spinning turbine blades to create a preferred direction of flow of vacuum impurities out of the volume of the chamber. There are several drawbacks to using these active vacuum pumps and these drawbacks become more significant under miniaturization for use in sensory applications based on optically cooled atoms.
Active pumps such as sputter ion pumps and mechanical turbo pumps have better pumping capability if they are large. Under miniaturization, the pumping capability of these active pumps is reduced to a point of diminishing returns. The large physical size of the active pump itself is a major limitation and dictates the ultimate size of the source. Furthermore, as cold atom vacuum chambers get smaller in size, the active pumps must be closer in proximity to the collections of cold and ultracold atoms. Stray magnetic fields from active vacuum pumps can have a detrimental effect on cold atom-based sensors. The effects of these stray fields are accentuated in smaller systems and it becomes increasingly difficult to shield the atoms from them. Elimination of such pumps can enable further miniaturization of ultracold atom sources and spur application development.
Traditional vacuum systems utilized in the production of optically cooled atoms and ultracold atoms (such as BEC) are large in size. It is common for these systems to weigh between 10 kg and 50 kg with length of about 1 meter in at least one physical dimension. These systems incorporate heavy suitcase-sized active pumps such as sputter ion pumps or mechanical turbo pumps to maintain the low pressures required for producing collections of cold and ultracold atoms. The required pressures can vary from as high as about 10−8 torr to about 10−13 torr depending on the goal of the apparatus. The chambers contain a mechanism to dispense the atoms of interest; typically alkali atoms such as rubidium or cesium. Atoms are dispensed into the chamber to form a low-density room-temperature vapor that can be cooled and confined in a magneto-optical trap (MOT). Traditional vacuum systems for producing ultracold matter can be based on a two-chamber design where the chambers are coupled using a narrow tube or aperture. A single-chamber design can also be used for optical cooling, however, the two-chamber design gives better vacuum performance albeit, at the cost of greater system size and complexity.
The present invention addresses the need for a miniature vacuum chamber with reduced reliance on active pumping to be used as a source for ultracold atoms. A UHV vacuum chamber is formed that eliminates or reduces the use of active vacuum pumps and further provides a simplified geometry for producing ultracold matter. The primary challenge in creating such a chamber is managing the permeation of substances, called vacuum impurities, into the vacuum chamber which add to the background pressure and spoil the necessary UHV conditions. Of particular concern is helium as a vacuum impurity. Helium is naturally found in the air and can readily diffuse through many window materials. Furthermore, helium is not effectively pumped by any passive getter material. The present invention provides a helium impervious window in a vacuum chamber used for atom cooling, trapping, and probing.